Novel multimedia devices are having multifunction applications. Phones and multimedia devices are used for connecting, finding, storing and spreading information via digital or audio channels (speech and listening). Such portable devices are used in different environments such as offices, silent cabinets, hospitals, metro, public but quiet places, etc., or in more noisy conditions as noisy streets, riding motorbike, etc. To satisfy sufficient quality of communications in all of these conditions the audio system has to provide a “silent input method” (do not disturb your environment while communicating) or it has to cancel noise from the surrounding environment (noise cancellation). The quality of communications is directly related to use conditions and limitations set by an audio-digital-audio signal conversion mechanism. Versatile usage conditions are difficult to cover by using present technical solutions for digital audio communications, which limits quality of information exchange and user satisfaction by products and services.
To improve audio conversion mechanisms, different technologies have been used. An example of a relatively new and direct conversion mechanism which avoids the air as sound wave propagation medium is a Silent Violin where vibrations from the wires are propagated through solid materials towards an ADC (analog-to-digital converter) for converting to a digital signal, which is then amplified and finally released into the air providing a beautiful sound quality.
Hardware (HW) miniaturization trends put size limits on both microphones and speakers challenging the quality of audio communications. Usually an audio signal propagates from the user's mouth to the air, to a microphone “listening” the air and then digitally converted and electrically amplified and finally spread into the air (e.g., by a speaker). The air is not the best medium for propagation of sound waves. Furthermore, the air is usually full of different sounds (noises) which are not useful while communicating by the portable electronic equipment. The air (gas mixture) is not the best medium, solid and liquid state materials are much more efficient in sound propagation. Moreover, the audio signal in the air has large dissipation requiring the user to speak relatively loudly to achieve a good quality of the audio communication. Therefore, a direct coupling of a microphone to a user body (avoiding the air) can present a very advanced solution for silent and not disturbing communications, such that the user does not disturb the environment while speaking (high sensitivity level) and the user is not disturbed by the environmental conditions (noise free communication).
Ordinary handsfree modules and hearing aids are very useful modules/gadgets. On the other hand, people do not like carrying separate modules while commuting and travelling. At the present, high-level integration technologies can provide a single small device which might be hosted at an external electronic device (e.g., mother phone).
In the available hands-free solutions, the background noise is clearly hearable to the receiver of the call. Certain algorithms are utilized in the noise reduction, but they can generally reduce the noise level only by 10-15 dB. However, the mobile devices are also used in circumstances, in which the noise level is high compared to the speech level. This poses a problem for the current sensor solutions (traditional pressure microphones) and, also, for actuator solutions (traditional loudspeakers). Moreover, often the users wish to protect their hearing under such conditions. For such protection either circumaural or insert-type ear-defenders are used. In both cases, the protection solution further complicates or prohibits the communication.